The polymerization of lower .alpha.-olefins to produce polyolefins is an industry of substantial significance. The polymeric products are of economic importance because of the relatively low cost thereof and the desirable properties they exhibit. However, to obtain polymers of commercially acceptable properties it is generally necessary to incorporate one or more additives into or onto the polymeric material. Such additives include thermo-oxidative stabilizers, U.V. stabilizers, processing stabilizers, acid acceptors and other materials chosen to modify the processability and properties of the polymeric substrate. The provision of such additives to the polymer does present some difficulty on occasion. One conventional method of incorporating additives such as stabilizers into a polyolefin polymer involves the extrusion step typically employed to produce the polymer in pellet form. Stabilizers are mixed with the polymer feed to the extruder and stabilized compositions are produced by the mixing associated with the extrusion. The resulting stabilized polymer is in the physical form of pellets and much of the commercial polyolefin, particularly polypropylene, is marketed in this form. The extrusion method, although widely practiced, has disadvantages in that the polymer and/or additive may degrade under the conditions of heat and shear encountered in the extrusion and the process is energy-intensive.
In U.S. Pat. No. 3,591,409 there is disclosed a method of coating resin particles which involves high intensity mechanical mixing of a polymer with additives and a binder. In U.S. Pat. No. 4,517,246 there is claimed a polymeric material which has been coated with additives and a binder through the use of a mechanical mixer. In Chatterjee, U.S. Pat. No. 4,960,617, there is disclosed a method of stabilizing polypropylene after passage from the polymerization reactor. This method involves application of additives dispersed in hot, molten wax. In U.S. Pat. No. 3,271,185 a process is described wherein vaporizable antioxidant is added to a fluidized bed of polymer. It would be of advantage, however, to provide an improved method of applying additives to polymeric materials, as well as the additive-incorporating polymer compositions produced by that process.